Composite fuse link



Feb. 5, 1957 M. M. LEAR, JR 2,780,696

COMPOSITE FUSE LINK Filed Oct. 6, 1953 INVENTOR Jim/144 426627; J51

BY ZM Q 26 ATTORNEYS United States Patent COMPOSITE FUSE LINK Max M. Lear, .lxu, Lakewood, N. Y., assignor, by mesne assignments, to Monarch Electric Corporation, Jamestown, N. Y., a corporation of Delaware Application October 6, 1953, Serial No. 384,502 6 Claims. (Cl. 200-135) This invention relates to electric fuse links, and is more particularly concerned with a composite structure of a fuse link which can be employed in an electric fuse for opening an electric circuit upon overloading.

A feature of the invention is the provision of a fuse link of parts which may be individually made to close tolerances and which upon assembly of the parts forms a fuse link of predetermined current-tolerating characteristics.

Another feature is the provision of a fuse link of pieces which have interfitting parts which can be assembled by riveting or upsetting the structure.

A further feature is the provision of a fuse made of parts which individually are constructed and arranged to transmit current up to a determined strength for a determined time: and which upon assembly provide a composite link having multiple current-time tolerances.

With these and other features as objects in view, an illustrative form of practice is shown on the accompanying drawings, in which:

Fig. 1 is a perspective view of the individual parts of a fuse link of this invention, arranged ready for assembly;

Fig. 2 is a sectional view, on an enlarged scale, showing the positioning of a terminal member on a central member;

Fig. 3 is a side elevation of the assembled fuse link, with parts broken away;

Fig. 4 is an axial section through a renewable fuse link holder, with the fuse link therein:

Fig. 5 is section similar to that of Pig. 4, of a cartridge type non-renewable fuse, with a modified fuse link therein.

The fuse link is illustrated as composed of two end members A, B and a central member C. The central member C is illustratively formed by die casting, with the end blocks 10, 11 identical and connected by the web or bridge 12. Each end block has a cavity provided by an annular groove 13 surrounding a central part 14 which extends above the general top level of the block and has its end formed with a conical cavity. From the groove 13 extends notch 15 of like depth leading to the edge of the block.

The terminal, or end members A, B are illustratively identical, and can be made from zinc sheet or strip stock by die press operations. Each member has a hole at one end, for fitting around a post 14; thus providing a ring portion 21 which enters a groove 15 with close tolerance. From this ring 21 extends a part 22 of uniform width for fitting the notch 15 with close tolerance. The other end of the member is of the same width as the blocks 10, l1; and has a hole 24. Between the longer end portions is the reduced neck or web portion 25.

The lengths of the parts, and the spacings of the posts 14, and of the holes 20, 24, are such that when assembled the holes 2 5 of the end members are spaced at the distance which is standard for the fuse cartridge in which the link is to be employed.

The members are assembled by placing an end mem- 2,780,696 Patented Feb. 5, 1957 her in position, with its hole 20 embracing a post 14; and then upsetting or riveting the material of the post, so that an enlarged outer end or head 30 is formed, Fig. 3, which clamps mechanically and forms electrically a secure joint between the members. The operation is repeated for the other end, and thus a firm and strong mechanical and electrical assembly is produced, with three neck or bridge portions 25, 12, 25 of reduced cross section.

Such a. link can then be employed for replacement of a blown link in a fuse cartridge, as shown in Fig. 4. The outer insulating sleeve 40 has two end caps 41, 42, shown in Fig. 4, through which extend the copper terminal blades 3 for engaging the clips of the fuse holder in usual fashion. These terminal blades 43 are connected inside of the sleeve 4 by an insulating spacer 44. The bolts 45, 46 bind the link ends, blade, and spacer together.

In the illustrative assembly, the reduced portions 25, 25, are located free of but close to the blocks 10, 11.

The central member C is preferably made of zinc by die-casting, for employments where the reduced portion 12 is to be melted or blown under one condition of operation of the link. When the portion 12 is not so to be utilized, other conductive materials may be employed therefor.

it will be noted that the blocks l0, 11, when assembled with the rings and adjacent parts of the end members, constitute heat-conducting bodies with larger radiation areas than the reduced portions 25, 12, 25, so that heat generated at the latter at current intensities below the fuse-blowing limit is transmitted to and held or dissipated by the blocks and also in part by the clamping parts including the bolts 55, and the blades 43. As the current intensity increases, a strength is attained at which the blocks and clamping parts are not able to dissipate the heat as fast as it is generated: and hence, at a time determined by the heat produced and the loss effects at the fuse-operating temperature, the fuse link attains a temperature at which one or another reduced portion is fused and volatilized, so that the circuit is opened. The rate of heat generation is controlled by the cross section of these reduced portions, as their individual resistances vary inversely with their sectional area and directly with their length. The heat capacity of the blocks and other parts is a function of their mass-volumes. Therefore, by selecting the dimensions of the parts, the delay condition of time at current strength" can be predetermined. The construction permits the blocks 10, 11 to be thicker than the web portions, so that they do not volatilize when the link fuses: this confinement of fusion to one or more web portions limits the evolution of metal from fused areas and is erfective to cause gravitational departure of the blocks from their normal functioning position with consequent increase of the arc length within the cartridge. In practice, it has been found that the burning extends only very short distances away from the reduced portions or webs.

Illustratively, for a ampere fuse (of 250 volt type) to open at 135 amperes load for minutes or less, and at 250 amperes load to open only after 20 seconds and in less than 30 seconds, employed in a cartridge having a spacing of the bolts 4-5, 46 of 3.312 inches, the central member C can have its blocks V2 inch wide. 0.105 inch thick and about 0.594 inch long; with the web 12 of section 0.125 by 0.055 inch and 0.125 inch long. The posts 14 are 0.250 inch diameter. The end members are of 0.020 inch stock, /2 inch wide, and the webs or bridges 25 are inch wide by 42 inch long.

The form illustrated in Figs. 1 to 4 shows the link employed as a renewable unit. The ability of easily attaining a link structure which operates accurately under at least two different conditions of amperage also lends itself to non-renewable fuses, as shown in Fig. 5. Here the pieces A, B, C are provided essentially as before. The blocks 10, 11 of piece C have the grooves 13 and notches 15 to receive the parts 21, 22 of the end pieces A, B, but the die-cast posts 14 are replaced by holes 114 for receiving bolts 115 which extend through the holes 2-3 of the end pieces and clamp the parts together. The end pieces A, B, in this illustrative modification, do not have the holes 24, and are originally formed as flat portions 123 as shown by dotted lines in Fig. 5 and coplanar with the parts 21., 22. The inner caps 141 have openings 143 in their end walls 14-2 for receiving these fiat portions 123 during assembly, and are illustratively secured to the insulating sleeve 140 by screwing onto the same. The ends of the portions 123 are then beat down to the fullline position in Fig. 5, and are soldered in place: the outer caps 1% threaded on the inner caps 14 i to complete the mechanical and electrical assembly and to close the openings 143 against direct passage of polls of hot gas when the fuse link operates. in this form, the pieces A, B, C may be of zinc.

The composition of the fuse link tnits change of dimension of one or demanding the preparing of a new casting die for each change. For example, if fuse links are to be made with longer or smaller webs at one or both ends, punch press die sets are made for the end member or members, different only in the spacings for forming the web. That is, stamping from sheets or strip will provide terminal members A, B competent to respond at a predeterminable amperage-time condition, e. g. within a maximum of 120 minutes at 135 amperes for a rated 100 ampere link.

A feature in operation is that when the current tolerance at one web or reduced portion is exceeded, and this web melts, the metal particles may permit a momentary arc; but this quickly is extinguished due to the initial combustion and filling with non-conductive oxides. Further, a current pulse at short circuit usually causes one or both of the other reduced portions likewise to melt so that series breaks are produced.

The illustrative forms are not restrictive; and the invention may be practiced in many ways within the scope of the appended claims.

1 claim:

1. A composite electric fuse link for use on a fuse link holder, a first member providing a heat-conductive and heat-absorbent mass and a portion fusible upon excessive current flow, a post integral with the first member and upstanding therefrom and an upstanding part spaced from said post; and a link terminal member bearing against the first member adjacent said post by an end portion thereof having a hole receiving said post, said link terminal member having an end for conductive engagement to said link holder, and also having a portion of reduced cross section between said. ends; said post being formed with an enlarged outer end engaged with the terminal member to hold the parts together, said link terminal member engaging said upstanding part and held thereby against rotation about the axis of the post,

A composite electric fuse link for use on a fuse link holder, comprising a first member providing a heatconductive and heatabsorbent mass and having a groove defining a post; and a terminal member having an end formed to fit said groove with a hole receiving said post and an end for conductive engagement with said holder, and a fusible portion of reduced cross section between said ends; said post being formed with an enlarged outer end engaged with the terminal member to hold the parts together.

3. A composite electric fuse link for use on a fuse of several parts peranother part without link holder, comprising a thick first member providing a heat-conductive and heat-absorbent mass and having in its surface a pair of grooves near the respective ends, each groove defining a post and having a notch leading to the end of the first member, said first member having a fusible portion of reduced cross section between said posts; a pair of thin terminal members each having an end formed to fit a said groove and its notch with a hole receiving the respective said post, and an end for conductive clamping to said link holder; said post being formed with an enlarged outer end engaged with the terminal member to hold the parts together with the terminal members being held against rotation about the corresponding posts by the walls of the notches.

4. A composite electric fuse link for use on a fuse lius holder, comprising a first member providing a heatconductive and heat-absorbent mass, said first member having a cavity in one face and a notch extending from the cavity to an edge of said face; a terminal member having an end conforming to said cavity and including a hole, an end for conductive clamping to said holder, and a portion of reduced cross section between said ends; and a securing means connected with said first member and extending in said cavity through said hole and having an enlarged outer end engaged with the terminal memher to hold the parts together.

5. A composite electric fuse link for use on a fuse link holder, comprising a first member having a pair of heat-conductive and heat-absorbent blocks of larger cross section, an integral Web connecting said blocks and being of lesser width and thickness, each block having annular groove in a face thereof and connected by a notch of like depth leading to the end of the block, the groove defining a post integral with the block; and a terminal member having a ring fitting said groove with a hole receiving the post, said ring having an extension fitting said notch, an outer end on the terminal member for conductive clamping to said holder, and a portion of reduced cross section between said extension and said outer end; said post having an enlarged outer end engaged with the terminal member to hold the parts together.

6. A composite electric fuse link comprising a first member having a pair of heat-conductive and heatabsorbent blocks of large cross section, an integral web connecting said blocks and being of lesser cross section, each block having a recess in one face thereof; a pair of terminal members each having at one end a portion located in said recess of a respective block, and each having another end for mechanical and electrical connection, each said terminal member having a reduced portion between its said ends for determining a current load at which the fuse will open; and means for holding said members and blocks mechanically and electrically connected.

References Cited in the file of this patent UNITED STATES PATENTS 

